Device for cooling waste gas

ABSTRACT

The invention relates to a device for cooling waste gas, comprising an inlet area ( 1 ) for guiding a flow of waste gas, an outlet area ( 2 ) for discharging the optionally cooled waste gas, and a longitudinal housing ( 1 ) for receiving exchanging means ( 13 ) for heat exchange. The flow of waste gas flows through the exchanging means ( 13 ) on the way from the inlet area to the outlet area. The inlet area ( 2 ) and the outlet area ( 3 ) are arranged respectively on end areas of the housing ( 1 ) which are opposite in relation to the longitudinal direction. The flow of waste gas flows through the exchanging means ( 13 ) on a first flow path ( 16 ) and also on a second flow path ( 17 ) which is counter thereto.

The invention relates to a device for cooling waste gas according to the preamble of claim 1.

Heat exchangers which serve to cool waste gases of an internal combustion engine are known in particular from the construction of motor vehicles. Known among these heat exchangers are designs which are referred to on the one hand as “I-flow” arrangements and on the other hand as “U-flow” arrangements. The former case relates to heat exchangers in which the inlet and outlet connections for the waste gas are arranged on opposite sides of an elongate housing, the waste gas flowing through the heat exchanger region only once in a longitudinal direction. In the latter arrangement, the waste gas flows through the heat exchanger in a back and forth direction, i.e. in the shape of a U, so that frequently the inlet region and the outlet region are arranged on the same side of an exchanger housing.

The object of the invention is to disclose a heat exchanger in which, with good flexibility with regard to the installation position of the heat exchanger, a good cooling power is achieved in a given overall space.

According to the invention, for a heat exchanger mentioned at the outset, this object is achieved by the characterizing features of claim 1. This ensures, in a given overall space, a longer flow path of the flow of waste gas along the exchanger means, thus allowing a high cooling power to be achieved.

In an advantageous configuration, the device is a waste gas cooler for an internal combustion engine of a motor vehicle. The device according to the invention can be used advantageously in particular in combination with the often narrowly defined overall spaces in the case of motor vehicle engines. This applies above all at defined positions of the connections of the waste gas lines.

In a preferred exemplary embodiment, the exchanger means comprise a plurality of tubes for guiding waste gas which extend in the longitudinal direction and are arranged in the housing. Also advantageously, the housing has connections through which a liquid coolant can flow. Overall, this forms an effective, overall space-optimized waste gas heat exchanger with liquid cooling in a tube bundle design. Alternatively thereto, the device according to the invention can however also be an air-cooled waste gas cooler.

Also advantageously, the tubes can each be secured in their end regions in common head pieces. This allows a waste gas cooler to be produced in a simple manner.

Preferably, a first group of the tubes is associated with the first flow path and a second group of the tubes is associated with the second flow path, thus providing an extended total flow route of the flow of waste gas in a simple manner.

In a particularly advantageous development, a waste gas channel is provided and is arranged in the longitudinal direction and substantially parallel to the tubes. The waste gas channel can in this case be a single channel having a suitable cross section for low-resistance guidance of the total flow of waste gas or else a divided channel or a bundle consisting of separate tubes. Advantageously, the waste gas channel is connected directly to the inlet region. Particularly preferably, the device comprises in this case a first deflection means for deflecting the flow of waste gas from the waste gas channel into the first flow path. Also advantageously, the device comprises a second deflection means for deflecting the flow of waste gas from the first flow path into the second flow path. Overall, this forms in a simple manner a compact heat exchanger in which the flow of waste gas is guided via two deflections firstly from the inlet region in the direction of the outlet region, then in the opposite direction and then again in the direction of the outlet region. The exchanger means for cooling the flow of waste gas are in this case arranged in the region of the first and the second flow path, wherein the waste gas channel does not necessarily serve to exchange heat. For a simple embodiment, the second deflection means can in particular preferably be configured as a curved sheet metal part.

It is generally preferable for the device to comprise an adjustment device for selectively guiding the flow of waste gas. This ensures increased flexibility during waste gas guidance. Particularly preferably, the adjustment device leads the flow of waste gas in a first end position into the first flow path and in a second end position into the outlet region. As a result, the adjustment device can be used to select whether or not the flow of waste gas flows through the cooling exchanger region. In the latter case, one waste gas channel can in particular have the function of a bypass line, wherein it has in the first end position of the adjustment device the function of a feed line to the exchanger means. For this purpose, provision is preferably made for the flow of waste gas not to be guided in the second end position through the exchanger means, thus substantially preventing cooling of the flow of waste gas in the second end position.

In a particularly simple and preferred embodiment, the adjustment device comprises a flap which can rotate about an axis. In order to achieve a particularly small design, provision is preferably made for a maximum angle of rotation of the flap to be not more than 40 degrees, in particular not more than approximately 30 degrees. This relatively small angle of adjustment allows a drive unit for the flap to be designed cost-effectively and simply. It is generally preferable for the adjustment device to be able to be driven via an actuator.

In a further preferred detailed configuration, the adjustment device comprises a spring, the spring allowing a restoring force to be exerted in the direction of an end position of the adjustment device. Advantageously, the spring is in this case configured as a coil spring, and a rotatable shaft of the adjustment device is arranged within the coil spring. In this way, a high restoring force of the adjustment device, for example a rotatable flap, can be provided compactly and effectively. This may be desirable especially when an actuator of the adjustment device applies its adjusting force predominantly in just one direction.

Particularly advantageously, the spring has a coating, in particular made of a plastics material. This prevents restriction of the spring caused by metal spraying around or welding beads such as are formed for example during the manufacture of the device.

Generally, the adjustment device is initially inserted during manufacture between separate housing parts, after which the housing parts are permanently welded to one another. During this welding process, the spring is often in an exposed position and can become blocked or damaged by welding beads. The coating of the spring can prevent this. Expediently, the coating can in this case be subjected to as high temperatures as possible, for which purpose the coating preferably comprises a polymer based on a fluorinated hydrocarbon, in particular polytetrafluoroethylene (PTFE). Such polymers having good surface slip and high heat resistance are known for example under the commercial name Teflon®.

If it is sufficiently heat-resistant, the coating can be preserved even after manufacture during operation of the waste gas coolers. This allows the frictional resistance of the spring wire, which is for example wound helically with mutually touching windings, to be reduced and any noise formation is avoided. In addition, the coating provides good protection of the spring from corrosion. In principle, the coating can however also be broken down by the operating temperatures or for example be removed by evaporation.

An alternative or additional embodiment provides a sleeve which at least partly covers the spring and forms a protective cover from metal drops which spray around during the production process.

A spring, protected in this way by coating and/or a sleeve, of an adjustment device can in principle advantageously be combined with any design of a waste gas cooler and is not limited to the particular design of the present device.

In a preferred combination with the aforementioned features of the device, the ratio of a length of the housing in its longitudinal direction to a largest diameter of the housing is less than 3.5, in particular less than approximately 3. This provides a particularly compact design, so that the device can be used universally.

Further advantages and features of a device according to the invention will emerge from the exemplary embodiment described hereinafter and also from the dependent claims.

A preferred exemplary embodiment of a device according to the invention will be described hereinafter and commented on with reference to the appended drawings, in which:

FIG. 1 is a three-dimensional view of a device according to the invention, looking onto the outlet region;

FIG. 2 shows the device from FIG. 1, looking onto the inlet region;

FIG. 3 is a three-dimensional sectional view of the device from FIG. 1, looking onto the outlet region;

FIG. 4 is a three-dimensional sectional view of the device from FIG. 3, looking onto the inlet region; and

FIG. 5 is a schematic sectional view of the device from FIG. 1 to FIG. 4.

The device for cooling a flow of waste gas according to the preferred exemplary embodiment is used in the engine compartment of a car. It has a housing 1 which is configured as an elongate body having a substantially rectangular cross section. In its longitudinal direction, there are arranged on one end side of the housing an inlet region 2 and on the opposing end side an outlet region 3. These end side regions 2, 3, which are also referred to as diffusers, each consist of compression-molded parts which are welded to the housing 1. In the regions of the connection, the housing 1 has slightly projecting thickenings 1 c.

A rectangular flange 2 a, by means of which a waste gas line originating from the internal combustion engine of the car can be connected to the device, is attached to the inlet region by welding. The outlet-side continuation of the waste gas line can be produced via a round flange 3 a welded onto the outlet region 3.

The housing 1 comprises two connections 1 a, 1 b via which a liquid coolant can flow through the heat exchanger housing 1 in a manner known per se.

An actuator 4, which is configured as a pressure box, is secured to the housing 1 via a holding metal sheet 5. A lifting rod 6 of the actuator 4 drives via a rotary lever 7 a rotary shaft 9 which is loaded with a restoring force via a spring 8. The rotary shaft 9 passes through the wall of the outlet region 3 and is rigidly connected to an adjustment flap 10 in the interior of the outlet region 3, so that rotation of the shaft 9 allows the adjustment flap 10 to be adjusted. All of the drawings FIG. 1 to FIG. 5 show the above-described drive mechanism and the adjustment flap 10 both in a first end position and in a second end position. The flap 10 rests in the first end position with its edge against the wall of the outlet region 3 and in the second end position against a small guiding metal sheet 19. Overall, the actuator 4, the rotary shaft 9 and the flap 10 form an adjustment device of the heat exchanger.

The spring 8 is configured as a coil spring made of a wound spring wire, the rotary shaft 9 passing through the windings. The ends of the spring winding are supported at one end against the housing and at the other end against the rotary lever 7, so that the spring applies force to the rotary shaft 9 in the direction of an end position of the adjustment flap.

The spring wire is coated over its entire length with PTFE (polytetrafluoroethylene, Teflon®). During manufacture of the waste gas cooler, the rotary shaft 9 is first pushed and secured through the spring 8 and wall of the outlet region, the adjustment flap 10 being welded to the rotary shaft. Subsequently, still further welding operations are carried out, for example the welding of the outlet region 3 onto the further housing 1. During these welding processes of the production process, liquid metal spraying around causes welding beads to accumulate in the environment of the immediate welding process. The PTFE coating prevents the welding beads from clinging to the spring 8. In addition, the PTFE has such high heat resistance that it is not broken down or even does not catch fire even in normal operation of the waste gas cooler.

The interior of the device is constructed as follows: The inlet-side flange 2 a opens into a cavity 2 b in the inlet region 2. The inlet region 2 is divided into the aforementioned cavity 2 b and a further cavity 2 c via a first deflection means 11. The deflection means 11 is configured as a curved metal sheet which, in order to simplify production, is welded on during assembly of the device.

A waste gas channel 12, which passes through the housing 1 in its longitudinal direction, adjoins the cavity 2 b. The waste gas channel 12 opens into a first portion 3 b of the outlet region 3. Although the waste gas channel 12 does in principle impart a certain cooling to the flow of waste gas, especially as its walls are thermally conductive, it is not configured so as to exchange heat with the liquid coolant, so that the flow of waste gas is cooled in the sense of the invention not substantially in the waste gas channel 12.

A plurality of tubes 13, which in the present example are configured as flat tubes having a rectangular cross section, are provided parallel to the waste gas channel 12. The plurality of tubes 13 and the waste gas channel 12, which is configured as a single tube having a much larger cross section, are jointly received between a respective end-side head piece 14, 15. These head pieces 14, 15 are strong holding metal sheets with corresponding punched-out portions for receiving the ends of the tubes. The head pieces 14, 15 are all tightly welded to the ends of the tubes and to the housing 1, thus forming between the head pieces and an outer wall of the housing 1 a cavity which remains between the individual tubes and through which the coolant can flow. Flowing around the waste gas channel 12 can in this case be prevented by further measures, depending on the desired cooling power of the waste gas channel 12. The coolant flows during operation around the tubes 13 which thus constitute exchanger means for exchanging heat for the waste gas.

In the case of the present invention, the plurality of tubes 13 are divided into a first group and a second group of tubes 13. In this case, the first group of tubes is associated with a first flow path 16 and the second group of tubes with a second flow path 17 (see the arrows indicating the flow paths in FIG. 5).

The bundle of tubes 13 is divided into two flow paths 16, 17 by a first deflection means 18 arranged in the outlet region 3. The deflection means 18 is arranged as a flow metal sheet between the head piece 15 and the shaft 9 of the adjustment flap 10. The deflection means 18 separates the first space 3 b of the outlet region 3 from a second space 3 c. The first space 3 b is located at the entry of the first flow path 16 and the second space 3 c is located at the exit of the second flow path 17.

The function of the device according to the invention may be seen particularly clearly from the view according to FIG. 5:

The flap 10 can be moved between two end positions, both of which are indicated for the sake of clarity, through approximately 25 degrees with respect to an angle of rotation of the shaft 9. The left-hand stop, as shown in FIG. 5, of the flap 10 corresponds to a first end position. In any case, the flow of waste gas is first led, after entering through the flange 2 a and flowing through the space 2 b, through the waste gas channel 12 in which, however, it experiences no or only slight cooling. Once the flow of waste gas has entered the space 3 b, there are various possibilities, depending on the position of the flap 10, for further guidance of the flow of waste gas. In the case of the first end position (left-hand stop), the flow of waste gas is led from the space 3 b into the first group of tubes or the first flow path 16. On this first flow path, the flow of waste gas passes through the housing 1 in the longitudinal direction, in the direction counter to the waste gas channel 12 (see the arrows in FIG. 5). At the end of the first flow path, the flow of waste gas enters the space 2 c of the first inlet region, where it is deflected through approximately 180 degrees. Afterwards, it enters the other bundle of tubes or the second flow path 17 on which it passes through the longitudinal direction of the housing 1, again in the opposite direction. After leaving the flow path 17, the flow of waste gas enters the space 3 c and afterwards the outlet flange 10. In the case of this first end position of the flap 10, the flow of waste gas passes through the heat exchanger means 13 thus on a U-shaped route, so that the total flow length along the surfaces of the cooled tubes 13 corresponds to approximately twice the length of the housing 1.

In the case of the second end position, which corresponds to the right-hand stop of the flap 10 in FIG. 5, the flow of waste gas is supplied, after flowing through the space 3 b, directly to the outlet flange 10 without the flow of waste gas flowing through the exchanger means or cooled tubes 13. In this mode of operation, the waste gas channel 12 has a function similar to bypass channels known per se of heat exchangers which are flowed through only in one direction. In the case of the first end position, in which the flow of waste gas is cooled, the waste gas channel 12 does not have the function of a bypass channel, but rather the function of a feed line to the exchanger means 13.

This arrangement provides a heat exchanger which has a very compact design and at the same time has at one of its ends an inlet region and at its other, opposing end an outlet region. As may be seen from the true-to-scale drawings, the length of the housing 1, including the inlet and outlet regions 2, 3, is in this case less than three times a maximum housing diameter in a direction perpendicular to the longitudinal direction. The dimensions and overhangs of the flanges 2 a, 3 a were not taken into account in this calculation. The flanges can also easily be made more compact, for example by directly welding the feeding and discharging waste gas tubes to the heat exchanger device. In particular, the relatively small angle of adjustment of the flap 10 between the two end positions contributes to the compact design of the device. 

1. A device for cooling waste gas, comprising an inlet region for supplying a flow of waste gas, an outlet region for discharging the optionally cooled waste gas, and a longitudinal housing for receiving exchanger means for exchanging heat, the flow of waste gas flowing through the exchanger means on a route from the inlet region to the outlet region, the inlet region and the outlet region each being arranged at end regions of the housing which are opposite in relation to the longitudinal direction, wherein the flow of waste gas flows through the exchanger means on a first flow path and also on a second flow path which is counter thereto.
 2. The device as claimed in claim 1, wherein the device is a waste gas cooler for an internal combustion engine of a motor vehicle.
 3. The device as claimed in claim 1, wherein the exchanger means comprise a plurality of tubes for guiding waste gas which extend in the longitudinal direction and are arranged in the housing.
 4. The device as claimed in claim 3, wherein the housing has connections through which a liquid coolant can flow.
 5. The device as claimed in claim 3, wherein the tubes are each secured in their end regions in common head pieces.
 6. The device as claimed in claim 3, wherein a first group of the tubes is associated with the first flow path and a second group of tubes is associated with the second flow path.
 7. The device as claimed in claim 3, wherein a waste gas channel is provided and is arranged in the longitudinal direction and substantially parallel to the tubes.
 8. The device as claimed in claim 7, wherein the waste gas channel is connected directly to the inlet region.
 9. The device as claimed in claim 8, wherein the device comprises a deflection means for deflecting the flow of waste gas from the waste gas channel into the first flow path.
 10. The device as claimed in claim 9, wherein the device comprises a further deflection means for deflecting the flow of waste gas from the first flow path into the second flow path.
 11. The device as claimed in claim 10, wherein the further deflection means is configured as a curved sheet metal part.
 12. The device as claimed in claim 1, wherein the device comprises an adjustment device for selectively guiding the flow of waste gas.
 13. The device as claimed in claim 12, wherein the adjustment device in a first end position leads the flow of waste gas into the first flow path and in a second end position leads it into an outlet opening.
 14. The device as claimed in claim 13, wherein the flow of waste gas in the second end position is not guided by the exchanger means, so that cooling of the flow of waste gas is substantially avoided in the second end position.
 15. The device as claimed in claim 12, wherein the adjustment device comprises a flap which can rotate about an axis.
 16. The device as claimed in claim 15, wherein a maximum angle of rotation of the flap is not more than approximately 40 degrees, in particular not more than approximately 30 degrees.
 17. The device as claimed in claim 12, wherein the adjustment device can be driven via an actuator.
 18. The device as claimed in claim 1, wherein the adjustment device comprises a spring, the spring allowing a restoring force to be exerted in the direction of an end position of the adjustment device.
 19. The device as claimed in claim 18, wherein the spring is configured as a coil spring.
 20. The device as claimed in claim 19, wherein a rotatable shaft of the adjustment device is arranged within the coil spring.
 21. The device as claimed in claim 18, wherein the spring has a coating, in particular made of a plastics material.
 22. The device as claimed in claim 21, wherein the coating comprises a polymer based on a fluorinated hydrocarbon, in particular polytetrafluoroethylene.
 23. The device as claimed in claim 18, wherein the spring is arranged within a sleeve covering the spring.
 24. The device as claimed in claim 1, wherein the ratio of a length of the housing in the longitudinal direction to a largest diameter of the housing is less than approximately 3.5, in particular less than approximately
 3. 